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biology paper 1 > cell transport > Flashcards

cell transport Flashcards

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1
Q

describe the fluid-mosaic model of membrane structure

A
  • molecules are free to move laterally in phospholipid bilayer
  • many components - phospholipids, proteins, glycoproteins and glycolipids
  • the membrane is fluid because the individual phospholipids can move relative to each other giving the membrane flexibility so is constantly changing shape
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2
Q

describe the arrangement of the components of a cell membrane

A
  • phospholipids form bilayer: fatty acids tails face inwards, phosphate heads face outwards
  • proteins (distributed throughout the membrane in a mosaic like pattern. the proteins vary in size/shape/pattern) :
    1. intrinsic/ integral proteins span full bilayer(plasma membrane) e.g. through channel and carrier protein
    2. extrinsic/peripheral proteins on surface of membrane and are partially embedded
    -glycolipids: lipids with polysaccharide chains attached which is found on exterior surface
    -glycoproteins: proteins with polysaccharide chains attached which is found on exterior surface
  • cholesterol: (sometimes present) bonds to phospholipid hydrophobic fatty acid tails
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3
Q

diagram with labels of the arrangement of the components of a cell membrane

A
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4
Q

explain the arrangement of phospholipids in a cell membrane

A

-plasma membrane separates 2 environments that are aqueous : BILAYER, with water present on either side
-hydrophobic fatty acid tails repelled from water so point away from water/ to interior
-hydrophilic phosphate heads attracted to water so point to water

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5
Q

explain the role of cholesterol (sometimes present) in cell membranes

A

restricts movement of other molecules making up membrane
so decreases fluidity (and permeability) / increases rigidity

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6
Q

suggest how cell membranes are adapted for other functions

A

phospholipid bilayer is fluid: membrane can bend for vesicle formation/phagocytosis
-glycoproteins/glycolipids acts as receptors/antigens: involved in cell signalling/recognition

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7
Q

describe how movement across membranes occurs by simple diffusion

A

-lipid-soluble (non-polar) or very small substances e.g. O2, steroid hormones and CO2
-move from an area on higher concentration to an area of lower
concentration: down a concentration gradient
-across a phospholipid bilayer
-passive: doesn’t require energy from ATP / respiration (only kinetic energy of substances)

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8
Q

explain the limitations imposed by the nature of the phospholipid bilayer

A

-restricts movement of water soluble (polar) and large substances e.g. Na+/glucose
-due to hydrophobic fatty acid tails in the interior of bilayer

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9
Q

describe how movement across membranes occurs by facilitated diffusion

A
  • water-soluble/polar/charged (or slightly larger) substances e.g. glucose, amino acids
  • move down a concentration gradient
  • through specific channel/carrier proteins
    -passive - doesn’t require energy from ATP / respiration (only kinetic energy of substances)
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10
Q

explain the role of carrier and channel proteins in facilitated diffusion

A
  • shape/charge of protein determines which substances move
  • channel proteins facilitate diffusion of water-soluble substances:
    1. hydrophilic pore filled with water
    2. may be gated - can open/close
  • carrier proteins facilitate diffusion of slightly larger) substances:
    1. complementary substance attaches to binding site
    2. protein changes shape to transport substances
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11
Q

describe how movement across membranes occurs by osmosis

A
  • water diffuses/ moves
  • from an area of high to low water potential (Ψ)/ down a water potential gradient
  • through a partially permeable membrane
  • passive : doesn’t require energy from ATP / respiration (only kinetic energy of substances)
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12
Q

what is water potential?

A

its the measure of how likely water molecules are to move out of a solution - pure (distilled) water has the maximum possible Ψ (0 kPA), increasing solute concentration decreases Ψ

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13
Q

describe how movement across membranes occurs by active transport

A

-substances move from an area of lower to higher concentration/ against a concentration gradient
- requiring hydrolysis of ATP and specific carrier proteins

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14
Q

describe the role of carrier proteins and the importance of the hydrolysis of ATP in active transport

A
  1. complementary substance binds to specific carrier protein
  2. ATP binds, hydrolysed into ADP + Pi, releasing energy
  3. carrier protein changes shape, releasing substance on side of higher concentration
  4. Pi released - protein returns to original shape
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15
Q

describe how movement across membranes occurs by co-transport

A
  • two different substances bind to and move simultaneously via a co-transporter protein (type of carrier proteins)
  • movement of one substance against its concentration gradient is often coupled with the movement of another down its concentration gradient
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16
Q

describe an example that illustrates co-transport

A

absorption of sodium ions and glucose ( or amino acids) by cells lining the mammalian ileum:
1. Na+ actively transported from epithelial cells to blood (by Na+/K+ pump). Establishing a concentration gradient of Na+ (higher in lumen than epithelial cell)
2. Na+ enters epithelial cell down its concentration gradient with glucose against its concentration gradient. Via a co-transporter protein
3. glucose moves down a concentration gradient into blood via facilitated diffusion
- the movement of sodium can be considered indirect/secondary active transport, as it is reliant on a concentration gradient established by active transport

17
Q

diagram of absorption of sodium ions and glucose(or amino acids) by cells lining the mammalian ileum

A
18
Q

describe how surface area, number of channel/carrier proteins and differences in gradients of concentration or water potential affect the rate of movement across cell membranes

A
  • increasing surface area of membrane increases rate of movement
    -increasing number of channel/carrier proteins increases rate of facilitated diffusion/active transport
  • increasing concentration gradient increases rate of simple/ facilitated diffusion- until number of channel/carrier proteins becomes a limiting factor as all in use/ saturated
  • increasing water potential gradient increases rate of osmosis
19
Q

explain the adaptions of some specialised cells in relation to the rate of transport across their internal and external membranes

A
  • cell membrane folded e.g. microvilli in ileum: increase in surface area
  • more protein channels/carriers: for facilitated diffusion (or active transport- carrier proteins only)
    -large number of mitochondria: make more ATP by aerobic respiration for active transport
20
Q

what are microvilli?

A

extensions of the cell membrane of some cells that are highly folded to increase surface area

biology paper 1 (7 decks)

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